Add a README to the types package.

packages/types/README.md

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+# Slack Types
+
+The `@slack/types` package is intended to be used as a central location for modeling Slack interfaces, types, payloads
+and constructs of all kinds.
+
+## Requirements
+
+This package supports Node v18 and higher. It's highly recommended to use [the latest LTS version of
+node](https://github.com/nodejs/Release#release-schedule), and the documentation is written using syntax and features
+from that version.
+
+## Installation
+
+```shell
+$ npm install @slack/types
+```
+
+## Usage
+
+This package exports a many different types and interfaces. It is best to peruse the source code to see what is
+available, but a brief list:
+
+- Block Kit blocks and elements (`./src/block-kit/*`)
+- Message attachments (`./src/message-attachments.ts`)
+
+## Getting Help
+
+If you get stuck, we're here to help. The following are the best ways to get assistance working through your issue:
+
+  * [Issue Tracker](http://github.com/slackapi/node-slack-sdk/issues) for questions, feature requests, bug reports and
+    general discussion related to this package. Try searching before you create a new issue.
+  * [Email us](mailto:developers@slack.com) in Slack developer support: `developers@slack.com`